Controlled braking of centrifuges is known, see, for example, German Disclosure Document DE-OS 26 40 745. Braking arrangements which are customary in various types of centrifuges, for example the type used for blood separation, require about 14 minutes after de-energization of the centrifuge motor. The customary blood separation small centrifuges operate at a speed of about 6000 rpm. It has not in the past been necessary to stop centrifuges, after the centrifuging operation, at a specific, short time, and the actual time required to brake the centrifuge was not material. New methods to obtain blood plasma, however, make it desirable to rapidly stop centrifuging operation. The method of blood separation to obtain blood plasma known as plasmapheresis provides return to the blood donor of the remaining components of the blood, particularly erythrocytes immediately after separation by centrifuging of the donated blood. The blood donor waits while the centrifuge operates adjacent the donor's bed or litter. It is thus of increasing importance to reduce the waiting time of the donor and any gain in time after centrifuging is complete and until the centrifuge is stopped, thus terminating the plasma separation, is of substantial advantage.